<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    .main {
        overflow: hidden;
    }
    .content {
        float: left;
        width: 100%;
        background-color:red;
    }
    .con {
        width: 100%;
        margin: 0 200px;
    }
    .left {
        float: left;
        width: 200px;
        background-color: blue;
        margin-left: -100%;
    }
    .right {
        float: left;
        width: 200px;
        background-color: green;
        margin-left: -200px;
    }
    </style>
</head>
<body>
    <div class="main">
        <div class="content">
            <div class="con">内容</div>
        </div>
        <div class="left">左边</div>
        <div class="right">右边</div>
    </div>
</body>
</html>